fix slf4j issues

Author: melaasar

build.gradle

@@ -5,7 +5,7 @@ buildscript {
 		gradlePluginPortal()
 	}
 	dependencies {
-		classpath 'org.xtext:xtext-gradle-plugin:3.0.2'
+		classpath 'org.xtext:xtext-gradle-plugin:4.0.0'
 		classpath 'io.opencaesar.ecore:ecore-bikeshed-gradle:+'
 	}
 }
@@ -34,6 +34,7 @@ subprojects {
 
 	dependencies {
 		api platform("org.eclipse.xtext:xtext-dev-bom:${xtextVersion}")
+		implementation 'org.slf4j:slf4j-simple:+'
 	}
 
 	java {

io.opencaesar.oml.dsl/pom.xml

@@ -41,6 +41,11 @@
 						<artifactId>xtext-antlr-generator</artifactId>
 						<version>2.1.1</version>
 					</dependency>
+					<dependency>
+						<groupId>org.slf4j</groupId>
+						<artifactId>slf4j-api</artifactId>
+						<version>2.0.17</version>
+					</dependency>
 				</dependencies>
 			</plugin>